I found that the boost from -85dB to -105 dB happened only after the modification of adding additional feedback & X connections.
The X resistors are becoming very value sensitive with a +20 dB performance peak at a certain point, while with only one X connection the values seem to be not very important.

There are now high impedance feedback connections from the output stage to every arm of the differential input amps, and low impedance feedback connections to every leg of the differential input amps.

The X connections may be like in the schematic or also crossed between the legs.